The vertebrae in a patient's spinal column are linked to one another by the disc and the facet joints, which control movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on the left side, and a pair of articulating surfaces located on the right side, and each pair includes a superior articular surface, which faces upward, and an inferior articular surface, which faces downward. Together the superior and inferior articular surfaces of adjacent vertebra form a facet joint. Facet joints are synovial joints, which means that each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing the joints to move or articulate relative to one another.
Diseased, degenerated, impaired, or otherwise painful facet joints and/or discs can require surgery to restore function to the three joint complex. Damaged, diseased levels in the spine were traditionally fused to one another. While such a technique may relieve pain, it effectively prevents motion between at least two vertebrae. As a result, additional stress may be applied to the adjoining levels, thereby potentially leading to further damage.
More recently, techniques have been developed to restore normal function to the facet joints. One such technique involves covering the facet joint with a cap to preserve the bony and articular structure. Capping techniques, however, are limited in use as they will not remove the source of the pain in osteoarthritic joints. Caps are also disadvantageous as they must be available in a variety of sizes and shapes to accommodate the wide variability in the anatomical morphology of the facets. Caps also have a tendency to loosen over time, potentially resulting in additional damage to the joint and/or the bone support structure containing the cap.
Other techniques for restoring the normal function to the posterior element involve arch replacement, in which superior and inferior prosthetic arches are implanted to extend across the vertebra typically between the spinous process. The arches can articulate relative to one another to replace the articulating function of the facet joints. One drawback of current articulating facet replacement devices, however, is that they require the facet joints to be resected. Moreover, alignment of the articulating surfaces with one another can be challenging.
Accordingly, there remains a need for improved systems and methods that are adapted to mimic the natural function of the facet joints.
US Patent Publication No. 2006/0142758 (“Petit”) discloses a linking element that consists of a helical spring and a support member made out of a polymer material. The helical spring is embedded in the support material.
US Patent Publication No. 2004/0215191 (“Kitchen”) discloses a flexible tube comprising at least one lumen that extends the length of the tube. At least one rod of a preformed curvature is present within said one lumen of the tube. As additional rods are placed within the hollow flexible member, increased force is applied to the spine by the device, thereby moving the spine towards the desired curvature.
US Patent Publication No. 2004/0049189 (“Le Couedic”) discloses a device that has two rigid rod-forming parts made of a first material. A connecting body that is made entirely from a second material that is more elastically deformable than said first material interconnects the two rod-forming portions.
US Patent Publication No. 2005/0065514 (“Studer”) discloses a dampening element comprising two spring elements coaxial with or parallel to a longitudinal axis, and two axially end-side connectors. The end-side connectors can be linked to the spring elements such that at least one of the spring elements is connected to the connectors. The two spring elements have different spring rates and one sprint element is designed as a tension and compression spring and comprises a spring coil, and the damping element is pre-stressed.
EP Patent Publication No. 0 677 277 (“Moreau I”) discloses a helically split oblong rotating member attached to upper and lower parts. The hollow central part of said member is filled at rest with a viscoelastic cushioning product cast in inter-thread overflow.
FR Patent Publication No. 2 717 370 (“Moreau II”) discloses an intervertebral stabilizing prosthesis comprising a hollow body of revolution that is radially and/or helically slotted to make it axially flexible, whose internal spaces and slots are filled with a viscoelastic product constituting an elastic shock-absorbing tensioner that is micrometrically adjustable. Yoke systems allow the assembly to be embedded by nuts into anchors and screwed into the bone.
GB Patent Publication No. 2 382 307 (“Sengupta”) discloses an assembly for soft stabilization of the spine comprising a pair of pedicle screws and a helical spring member. The helical spring member may be made from titanium or stainless steel. A plastic sleeve may or may not cover the spring.
US Patent Publication No. 2005/0203517 (“Jahng”) discloses an elastomer cladding on a wire.
U.S. Pat. No. 6,989,011 (Paul) discloses a device containing a spring and two ends, where the ends and the spring are integrally formed.
US 2006/0041259 (Paul) discloses a dynamic device containing at least one spring integrally formed to the substantially solid ends.
US 2003/0109880 (Shirado) discloses a resilient PDS member with anchors.
U.S. Pat. No. 6,761,719 (Justis) discloses a device for stabilizing at least a portion of the spinal column, including a longitudinal member sized to span a distance between at least two vertebral bodies and being at least partially formed of a shape-memory material exhibiting pseudoelastic characteristics at about human body temperature. A number of bone anchors are used to secure the longitudinal member to each of the vertebral bodies. The longitudinal member is reformed from an initial configuration to a different configuration in response to the imposition of stress caused by relative displacement between the vertebral bodies, and recovers toward the initial configuration when the stress is removed to thereby provide flexible stabilization to the spinal column. During reformation of the longitudinal member, at least a portion of the shape-memory material transforms into stress-induced martensite. In a particular aspect of the invention, the longitudinal member is a plate having a central portion at least partially formed of the shape-memory material, and a pair of connection portions disposed at opposite ends of the central portion for connection to each of the vertebral bodies. The central portion of the plate defines a number of alternating ridges and grooves along a length thereof having an initial amplitude corresponding to the initial configuration and a different amplitude corresponding to the different configuration.
US 2004/0236329 (Panjabi) discloses a dynamic rod device with greater resistance to movement during the central zone and lower resistance to movement as it extends beyond the central zone, i.e. neutral zone theory.
US 2005/0171543 (Timm) discloses a pedicle based dynamic stabilization system.
US 2006/0036240 (Colleran) discloses a dynamic device allowing controlled motion and disc off loading.
US 2008/0033435 (Studer) discloses a dynamic device with two springs and a dampening element where the two springs have different spring constants.
US 2006/0282080 (Albert) discloses a dynamic device with a spring element.